The present invention relates to a measurement system using laser beams.
Some of the measuring systems utilizing the high power and high directability of laser beams are rangefinders measuring distances to targets, laser radars measuring the molecular composition of the atmosphere, etc., and other systems. These systems transmit very strong laser beams. If there is a scattering surface or a man at a short distance in the path of the transmitted beam, therefore, a strongly-scattered beam is returned to the beam receiver, which could damage an optical detector and the eyes or skin of humans. Even when no damage is inflicted on the components of the receiver, the strong return beam can exceed the dynamic range of the optical detector and amplifier, etc., making it impossible to obtain specific reception signals from a target located at a short distance.
In conventional systems, accordingly, the absence of scattering surfaces or humans in the path of the transmitted beam is confirmed visually to ensure safety prior to the actual measurement, and if there is any scattering surface or the like in the path, an attenuator is put in a beam receiver unit for the measurement. This makes it difficult to carry out a rapid measurement, and it also necessitates the provision of an attachment such as nocturnal vision apparatus at night, since unaided visual confirmation is impossible then.